From - Fri Nov 30 08:49:16 2001
Delivered-To: postfix-users@cloud9.net
Subject: Re: Free RBL services??
Reply-To: postfix-users@postfix.org (Postfix Users List)

> Subject: Re: Free RBL services??
>
> The RFC only says the EHLO/HELO argument must be a FQDN,
> not that it must actually resolve.

So you might think if you read only part of the specification, but in
the whole context you're flat-out wrong.  Although RFC 821 and RFC 1123
were written a long time ago before people learned to frequently
misinterpret things so frequently, this one (RFC 1123) is really Really
REALLY hard to mis-interpret:

      5.2.5  HELO Command: RFC-821 Section 3.5

         The sender-SMTP MUST ensure that the <domain> parameter in a
         HELO command is a valid principal host domain name for the
         client host.  As a result, the receiver-SMTP will not have to
         perform MX resolution on this name in order to validate the
         HELO parameter.

         The HELO receiver MAY verify that the HELO parameter really
         corresponds to the IP address of the sender.
[...]
how could you possibly not make the connection between "valid principal host
domain name" and "corresponds to the IP address of the sender"!?!?!?!?